The present invention relates to a control circuit, and more particularly to a control circuit for use with a switch power converter.
FIG. 1 is a diagram illustrating circuit functional blocks of a conventional switch power converter. As shown in FIG. 1, the switch power converter 1 includes a bridge rectifying circuit 11, a filter circuit 12 for avoiding the electromagnetic wave interference, a transformer with its peripheral circuit 13, a DC output circuit 14, a controlled switch circuit 15, a feedback circuit 16 and a control circuit 17. The AC power 10 is transformed to a DC voltage via the switch power converter 1, and then the DC voltage is provided to a load 18. The feedback circuit transfers the variation state of the current density or the voltage value at the output end to the control circuit 17. Hence, the control circuit 17 will generate a control signal which is outputted to the controlled switch circuit 15 in response to the state of the current density or the voltage value for determining the working condition of the transformer and its peripheral circuit 13. Therefore, the switch power converter 1 can provide a proper DC power for the load 18.
For the conventional switch power converter, a pulse bandwidth modulating IC is used to achieve the function of the control circuit. As known, the pulse bandwidth modulating IC will still keep producing a modulating signal of a very small pulse bandwidth even when the conventional switch power converter is free from load to consume power. Hence, the power will keep losing. In addition to the power loss, the control circuit using the pulse bandwidth modulating IC also has the disadvantages of high cost and large volume.
Therefore, the purpose of the present invention is to develop a control circuit for use with a switch power converter to deal with the above situations encountered in the prior art.
An object of the present invention is to provide a control circuit for use with a power switch converter for avoiding the power loss when the power switch converter is operated without loading.
Another object of the present invention is to provide a control circuit for use with a power switch converter for reducing the size of the power switch converter.
A further object of the present invention is to provide a control circuit for use with a power switch converter for reducing the cost.
According to an aspect of the present invention, there is provided a control circuit for use with a switch power converter. The switch power converter includes a rectifying circuit, a transformer with a peripheral circuit, a DC output circuit, a controlled switch circuit and a feedback circuit for transforming an AC power to a DC voltage provided to a load. The control circuit includes a capacitor device electrically connected between a variable resistor of the feedback circuit and ground in series, the variable resistor has a resistance varying with a voltage value of the load, a first divider resistor electrically connected between the variable resistor and the controlled switch circuit in series, a second divider resistor electrically connected between the first divider resistor and ground in series, and a controlled switch electrically connected among the controlled switch circuit, the first divider resistor and ground, wherein an overall voltage value of the first and second divider resistors varies with the resistance of the variable resistor to switch the controlled switch for further optionally enabling the controlled switch circuit to allow the transformer with the peripheral circuit to process an energy transformation.
Preferably, the variable resistor electrically connected to the capacitor device in series is a transistor portion of a photo-coupler.
For example, the controlled switch can be a transistor. The controlled switch is preferably a bipolar junction transistor.
Preferably, the controlled switch is electrically connected to a switch of the controlled switch circuit. For example, the switch can be a metal oxide semiconductor field effect transistor (MOSFET).
Preferably, when the overall voltage value of the first and second divider resistors increases with the decrease of the voltage value of the load, the overall voltage value of the first and second divider resistors decreases to result in turning the controlled switch off and further enabling the controlled switch circuit to allow the transformer with the peripheral circuit to process the energy transformation, and when the overall voltage value of the first and second divider resistors decreases with the increase of the voltage value of the load, the overall voltage value of the first and second divider resistors increases to result in turning the controlled switch on and further disabling the controlled switch circuit to stop the transformer with the peripheral circuit processing the energy transformation.
According to another aspect of the present invention, there is provided a control circuit for use with a switch power converter. The switch power converter includes a rectifying circuit, a transformer with a peripheral circuit, a DC output circuit, a controlled switch circuit and a feedback circuit for transforming an AC power to a DC voltage provided to a load. The control circuit includes a capacitor device electrically connected between a variable resistor of the feedback circuit and ground in series, the variable resistor has a resistance varying with a voltage value of the load, a divider resistor electrically connected between the variable resistor and the controlled switch circuit in series, and a controlled switch electrically connected among the controlled switch circuit, the divider resistor and ground, wherein a voltage value of the divider resistor varies with the resistance of the variable resistor to switch the controlled switch for further optionally enabling the controlled switch circuit to allow the transformer with the peripheral circuit to process an energy transformation.
Preferably, the variable resistor electrically connected to the capacitor device in series is a transistor portion of a photo-coupler.
For example, the controlled switch can be a transistor. The controlled switch is preferably a bipolar junction transistor.
Preferably, the controlled switch is electrically connected to a switch of the controlled switch circuit. For example, the switch can be a metal oxide semiconductor field effect transistor (MOSFET).
Preferably, wherein when the voltage value of the divider resistors increase with the decrease of the voltage value of the load, the voltage value of the divider resistor decreases to result in turning the controlled switch off and further enabling the controlled switch circuit to allow the transformer with the peripheral circuit to process the energy transformation, and when the voltage value of the divider resistor decreases with the increase of the voltage value of the load, the voltage value of the divider resistor increases to result in turning the controlled switch on and further disabling the controlled switch circuit to stop the transformer with the peripheral circuit processing the energy transformation.
According to an additional aspect of the present invention, there is provided a control circuit for use with a switch power converter. The switch power converter includes a rectifying circuit, a transformer with a peripheral circuit, a DC output circuit, a controlled switch circuit and a feedback circuit for transforming an AC power to a DC voltage provided to a load. The control circuit includes a capacitor device electrically connected between a variable resistor of the feedback circuit and ground in series, the variable resistor has a resistance varying with a voltage value of the load, a first divider resistor electrically connected between the variable resistor and the controlled switch circuit in series, a second divider resistor electrically connected between the first divider resistor and ground in series, and a controlled switch electrically connected among the controlled switch circuit, the first divider resistor and ground. When an overall voltage value of the first and second divider resistors increases with the decrease of the voltage value of the load, the overall voltage value of the first and second divider resistors decreases to result in turning the controlled switch off and further enabling the controlled switch circuit to allow the transformer with the peripheral circuit to process the energy transformation. When the overall voltage value of the first and second divider resistors decreases with the increase of the voltage value of the load, the overall voltage value of the first and second divider resistors increases to result in turning the controlled switch on and further disabling the controlled switch circuit to stop the transformer with the peripheral circuit processing the energy transformation.